1. Field of the Invention
The present invention relates to a fixing device and an image forming apparatus.
2. Discussion of the Background
A conventional practice widely employed in electrographic image forming apparatuses is to convey a recording sheet of paper loaded with an unfixed toner image into a fixing nip region defined between a heater to be heated by a heat source and a pressurizer in contact with the heater. The recording sheet of paper is heated and pressed in the fixing nip region so as to fix the unfixed toner image to the recording sheet of paper. The heater for this kind of fixing device uses a thin heat generating member such as a heat generating belt, considering that the thin heat generating member has a small heat capacity, is capable of heating up in a short time, and consumes less energy.
An example of the heat generating source for the heat generating belt is a resistance heating element. The resistance heating element implements Joule heating upon establishment of electrical continuity. Japanese Unexamined Patent Application Publication No. 2009-109997 discloses a fixing device made up of this resistance heating element as a heat generation source and a heater. The heater includes a press roller (fixing roller) that has an outer diameter smaller than the inner diameter of a circumferentially driven endless fixing belt (heat generating belt), and that is loosely fitted to the inside of the fixing belt. The fixing device disclosed in Japanese Unexamined Patent Application Publication No. 2009-109997 has what is called a “clearance fit configuration”, that is, the press roller inside the fixing belt is pressed by a pressure roller from outside the fixing belt so as to define a fixing nip.
With the fixing device of Japanese Unexamined Patent Application Publication No. 2009-109997, the fixing belt comes into contact with the press roller on the upstream side of the fixing nip region in a recording-paper conveyance direction (inlet side of the fixing nip region). On the downstream side of the fixing nip region in the recording-paper conveyance direction (outlet side of the fixing nip region), the recording sheet of paper is heated under low pressure. This can cause poor image quality, such as uneven brightness, of the image after subjected to fixing. Additionally, the inclination angle (separation angle) of the fixing belt on the outlet side of the fixing nip region is small, and this can cause poor separatability of the recording sheet of paper past the fixing nip region.
The present invention has been made in view of the above-described circumstances, and it is an object of the present invention to provide a fixing device and an image forming apparatus including the fixing device. The fixing device provides satisfactory separatability of a recording sheet of paper after subjected to toner image fixing, and consumes less energy.